ROT13 & Caesar Cipher
Rotate letters by any shift. ROT13 is its own inverse, so one button both hides and reveals.
Input
Output
What ROT13 is for
ROT13 shifts every letter thirteen places along the alphabet. Thirteen is half of twenty-six, so applying it a second time brings the text back — one operation is both the encode and the decode.
It is not encryption and was never meant to be. It exists to stop text being read *accidentally*: a puzzle answer, a spoiler, a joke punchline. Anyone who wants to read it, can.
ROT47 does the same thing across the whole printable ASCII range rather than the letters alone, so digits and punctuation move too. That makes it useful where ROT13 leaves too much readable — a URL under ROT13 still shows its slashes and dots.
Caesar with any shift
A shift other than thirteen is a Caesar cipher, and is no longer its own inverse: encoding with +7 needs −7 to undo. With only twenty-five possible shifts, breaking one by trying them all takes seconds, which is why it survives as a teaching example rather than as a cipher.
Frequently asked questions
Does ROT13 protect anything?
No. It is a reversible letter substitution with no key, so anyone can undo it. Use it to avoid spoiling something, never to keep a secret.
Why are my Korean or Japanese characters unchanged?
ROT13 is defined over the 26-letter Latin alphabet, so anything outside it passes through untouched. ROT47 covers printable ASCII, which is still Latin-only.